1. Field of the Invention
The present invention relates to a protecting film for a substrate surface and more specifically to a protecting film for a substrate surface which is appended to the surface of the substrate for protecting it upon grinding a back of the substrate, as well as a method for grinding a back of a substrate by using the protecting film for a substrate surface.
2. Description of Related Art
Upon grinding a back of a wafer, a protecting tape made of a polyolefinic synthetic resin has been appended to a surface of the wafer for protecting the surface of the wafer on which a pattern is formed. Existent steps for grinding the back of the wafer are to be explained with reference to FIG. 1A to FIG. 1D.
At first, as shown in FIG. 1A, a wafer 1 having a pattern-formed layer 2 on a surface is provided and a protecting film 3 is appended on the surface (refer to FIG. 1B). Then, the back 4 of the wafer is ground by a grinding device (refer to FIG. 1C). Subsequently, after peeling the protecting tape 3 appended on the surface of the wafer 1 by a tape peeler (refer to FIG. 1D), the wafer is cleaned by a cleaning device using isopropanol as a cleaning liquid.
A method of peeling the protecting film by the tape peeler will be explained more specifically with reference to FIG. 2. For peeling the protecting tape 3, an orientation flat of the wafer 1 (usually referred to as ori-fla) is at first aligned to a positioning line on a peeling stage 5, and the wafer is placed with the protecting tape 3 being on the upper side to the peeling stage 5 of the tape peeler and adsorbed in a direction of an arrow (FIG. 2A). Then, a releasing tape 6 is placed on the protecting tape 3, and an append roller 7 is urged under rolling to append the peeling tape 6 on the protecting tape 3 (refer to FIG. 2B). Successively, an excess portion of the peeling tape 6 is laid over the appended portion of the releasing tape, and the excess portion is pulled to peel the protecting tape 3 together with the peeling tape 6 (refer to FIG. 2C). Finally, the wafer 1 is separated from the peeling stage 5 and contained in a cassette to complete a tape peeling operation.
The wafer ground at the back has an extremely low mechanical strength, so that it chips easily or causes partial depletion when undergoing even a small external force. Accordingly, upon conducting the peeling operation to the protecting tape, when the peeling tape is urged onto the protecting tape by the append roller, or when the excess portion of the peeling tape is pulled to peel the protecting tape together with the peeling tape, the wafer often suffers from damages, and the rate of occurrence for wafer chipping reaches as high as about 0.03% based on the entire number of wafers even at the present in which the grinding thickness for the wafer is 400 .mu.m.
On the other hand, along with a demand for reducing the thickness of semiconductor devices, it has become necessary to reduce the grinding thickness for the wafer to less than 300 .mu.m. Such a thin-walled wafer further suffers from a reduction of the strength against the external force and is damaged easily when undergoing even a slight force; thus, it is considered that the rate of occurrence for wafer chipping will amount to about 5%.